Efficient reconditioning of waste oils for reuse, so called recycling, is advantageous from both economic and ecological points of view. Use of reconditioned or recycled oils (hereafter reprocessed waste oil) as fuel or propellant is subject to governmental regulation in most countries because impurities therein may be released into the atmosphere creating an environmental hazard. In some cases, e.g., fuel oil applications, the impurity combustion products are most hazardous. Similar problems exist in other reprocessed waste oil applications, e.g., if they are used as base oil for the manufacture of lubricant oils.
The reprocessed waste oil impurities most commonly regulated for environmental reasons include inorganic and organic compounds of metals, of sulfur, of phosphorus, and the halogens, in particular of chlorine. Limiting the concentration of these impurities is particularly important when the reprocessed waste oil is to be used as base oil for the manufacturing lubricant oils.
Halogen compound concentration in reprocessed waste oil particularly chlorine compounds is of special importance because:
1. the halogen compounds present in the waste oils and their combustion products may be harmful to man and the environment;
2. the legal limits for the chlorine content of heating oils are very low; and
3 the efficient removal of high boiling point organic halogen compounds (e.g., chlorine) down to residual contents of less than about 100 mg chlorine/kg oil from waste oils has not been economically practical.
Conventional methods for the reprocessing of waste oils may involve acid treatment of the waste oil followed by a separation and neutralization of the resultant acid phase, and a thermal treatment step in which volatile fractions are driven off by distillation. In certain applications the reprocessed waste oils themselves are subsequently distilled.
Waste oil feedstocks such as used motor oil, typically contain about 1,000 to 10,000 mg or more of halogen per kg and are not adequately freed of halogens by the above conventional methods unless they are subjected to further treatment.
There are known methods that can remove halogen impurity from waste oils down to a concentration of about 100 mg/kg (expressed as chlorine Cl.sub.2). These methods include, e.g., an after-treatment with additives which bind chlorine, such as alkali or alkaline earth metals, alkali or alkaline earth hydrodixes such as sodium or potassium hydroxide solution or calcium or magnesium hydroxide or alkali hydroxides in combination with selected solvents, and/or may involve hydrogenation processes.
These methods have one or more of the following disadvantages:
1. they do not lower the residual halogen content to below about 100 mg/kg (expressed as chlorine);
2 they require high temperatures that may effect considerable thermal breakdown of the treated waste oils;
3 the remaining halogen and reaction products can be present in a form difficult to separate, e.g., a sludge which is difficult to filter or to centrifuge;
4 they can give rise to hazardous residues which create additional disposal problems;
5 added halogen binding agents can significantly increase the ash content of the recycled waste oils; and
6. they require special safety devices and/or precautionary measures due to the chemicals used.
Hence the above described methods are not economically and/or technically practical for reducing the halogen content of the waste oil on a large scale.
U S. Pat. No. 3,930,988 is directed to a method for the reduction of the ash and metals content in used lubricating oils in which the used oil is contacted with an aqueous solution of ammonium sulfate and/or ammonium bisulfate at about 93.degree. to 260.degree. C. and about 750 psig to react with the metal compounds present thus forming separable metal containing solids. The reaction mixture is separated into an aqueous phase containing the solids and an oil phase having reduced metals and ash contents.
U.S. Pat. No. 3,879,282 is directed to a method for decreasing the ash and lead content in used motor oils wherein the used oil is brought into contact with an aqueous solution of ammonium phosphate which forms insoluble metal salts which are allowed to settle as precipitate. Thereafter, an oil product phase separated from the aqueous phase and precipitate.
U.S. Pat. No. 4,151,072 is directed to a method for reclaiming used lubricant oils regardless of contaminants or additive systems (impurities) contained therein, wherein, e.g., (a) used oil is contacted with an aqueous solution of an ammonium salt treating agent such as a salt selected from the group consisting of ammonium sulfate, ammonium bisulfate, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate and mixtures thereof in appropriate quantities at a temperature of 60.degree. to 120.degree. C. (b) removing a major portion of the water and light hydrocarbons from the mixture of step (a) at a temperature of 110.degree. to 140.degree. C.; (c) separating the resulting oil phase by filtration; (d) heating the filtered oil phase to a temperature of 200.degree. to 480.degree. C. and contacting it with an adsorption agent. For some applications the resulting oil may be hydrogenated with hydrogen and a catalyst and then stripped at a temperature of 280.degree. to 395.degree. C.
DE-AS 25 08 713 is directed to a method for reprocessing used mineral oil involving pre-purification by means of coagulation, adsorption, filtration, distillation and a hydrogenation after-treatment. After the pre-purification the oil is dehalogenated, fractionated, distilled, and hydrogenated. Dehalogenation is effected by treatment of the waste oil with an alkali metal, in particular Na or K, an alkaline earth metal, in particular Mg or Ca, an alkali, alkaline earth or aluminum alcoholate, and alkali hydride or alkali amide, an organic base, in particular pyridine or piperidine or with metallic aluminum or anhydrous aluminum chloride under conditions that exclude air and moisture, at a reaction temperature of 15.degree. to 300.degree. C.
DE-OS 36 37 255 is directed to a method for the reprocessing of waste oil wherein the waste oil is mixed at a pressure of 50.degree. to 250 bar with a hydrogenous gas; at a reaction temperature of 350.degree. to 500.degree. C.; and solids are removed as sludge. An evaporated, oil-containing phase is withdrawn from the sludge and catalytically hydrogenated at temperatures of 300.degree. to 400.degree. C., the hydrogenated product is mixed with ammonia and degassed, and an ammonium chloride-containing aqueous phase is separated from the degassed product.
DE-OS 36 31 175 is directed to a method for the dehalogenation of hydrocarbon oils in which the hydrocarbon oils in a homogenous phase are treated at 120.degree. to 400.degree. C. with alkali or alkaline earth alcoholate having alkyl groups which contain 6 to 25. C atoms and the resultant alkali or alkaline earth halogenides are separated following the reaction.
DE-PS 36 00 024 is directed to a method for producing high-quality lubricant oils from waste oils through the catalytic hydrogenation of purified oil mixtures. The purified oil mixtures are freed of solids, as well as other dissolved and/or emulsified admixtures. The hydrogenating treatment is carried out in the presence of a commercially available hydrocracking catalyst at temperatures of 350.degree. to 480.degree. C. and pressures of 20 to 400 bar.
United Kingdom Patent No. 856,764 is directed to a method for decreasing the acidity of used lubricant oil wherein the oil is treated with ammonia.
The above-cited methods are either costly or otherwise lead to inefficient reprocessing of waste oils. Objects and Summary of the Invention